High speed rotating apparatuses, such as high frequency electric generators are often driven by low frequency electric motors or internal combustion engines. In such cases a speed increasing gear box is needed. When the apparatus is driven by a high speed gas turbine, often a speed reducing gear box is needed. Portable grinding and cutting rotating tools are usually driven by high speed pneumatic or electric motors. Sometimes, such tools require a flow of liquid coolant to prevent overheating and also to prevent metal sparks form igniting adjacent materials. Consideration of weight and power output of such tools is very important to its portability.